The present invention relates to the generation of drive signals in the recording apparatus and other related devices.
The recording apparatus in which liquid crystal light shutters are employed is intended to carry out light writing on a recording body in such a way that a plurality of micro shutters in the liquid crystal light shutter are driven open or closed by a control circuit so as to transmit or shield the light of a light source. Liquid crystal needs so as to have high speed response in the case of this recording apparatus. Therefore, the liquid crystal light shutter is usually formed by a liquid crystal material whose dielectric anisotropy is inverted by the frequency of an electric field, and it is driven by two frequencies f.sub.H and f.sub.L, higher and lower, resectively, than a frequency f.sub.C which makes the dielectric anisotropy of the liquid crystal zero. Therefore, the conventional control circuit for the liquid crystal light shutter is provided with two oscillators for generating the signals of the frequencies f.sub.H and f.sub.L, and with a generator for generating pattern signals which are formed by various combinations of f.sub.H and f.sub.L.
In FIG. 1, a read-only memory (which will be hereinafter referred to as ROM) 1 applies a data signal 4 to a flip-flop 5 when it receives an address A signal 2 for reading out the information of the ROM 1 and an address B signal 3 which contains a step signal. The flip-flop 5 advances step by step, synchronously with a clock signal 6, and outputs a needed pattern signal 7. The flip-flop 5 also outputs the address B signal 3 at the same time to select optional addresses in the ROM 1, thereby enabling complicated control to be achieved.
In the case of the conventional recording apparatus, the viscosity of liquid crystal shows remarkable change, depending upon temperature. Therefore, the voltage of signals applied to the liquid crystal light shutters is changed, corresponding to temperature change, to compensate the temperature of liquid crystal. Further, the temperature compensation of liquid crystal is sometimes attained by changing the frequencies of signals of f.sub.H and f.sub.L applied to the liquid crystal light shutters.
The conventional recording apparatus employs random logic which represents combinations of gate circuits for generating pattern signals, but the characteristics of light shutters, recording bodies, light sources, etc., change depending upon circumferential conditions and combinations of means, thereby making it necessary to sometimes change the pattern signal. The logic circuit which generates only the fixed pattern signals cannot meet the needs and so it must be recombined again. In the case where the light shutters are improved after the completion of a logic circuit, for example, it is necessary to again recombine or reconstruct the completed logic circuit.
On the other hand, when the voltage of the signal applied to the liquid crystal light shutters is changed in the case where circumferential temperature changes occur, the driven operation of the liquid crystal light shutters may become unstable. In addition, changing the frequency of signal f.sub.H by a large measure cannot achieve great effect when the temperature changes remarkably.